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Current Issue  
2019 Vol. 33, No. 4
Published: 2019-08-28

2018: The Hottest Summer in China and Possible Causes
Ting DING, Yuan YUAN, Jianming ZHANG, Hui GAO
2019, 33(4): 577-592 [Abstract]( 223 ) HTML PDF (5381 KB)  ( 2107 Supplemental Material
Abstract:In 2018, China experienced the hottest summer since 1961. The maximum, mean, and minimum temperatures all reached the highest. Air temperatures in most regions were much higher than normal; in northern China especially, the temperature anomalies were above double of the standard deviations. Consistent variations of temperature anomalies appeared in the national mean and in northern China on different timescales from intraseasonal to annual, indicating that the above normal temperature in northern China contributed significantly to the record-breaking hot summer of entire China. Relationships among the high temperature in summer 2018, the tropospheric circulation, and the global sea surface temperatures (SSTs) are further analyzed. It is found that the intensified and more northward western Pacific subtropical high (WPSH), weakened Northeast China cold vortex (NECV), and positive geopotential height anomaly from northern China to the Sea of Japan resulted in the abnormally high temperature in summer 2018. From late July to mid August, the WPSH was stronger than normal, with its ridge line jumping to north of 40°N; meanwhile, the NECV was much weaker and more northward than normal; both of the two systems led to the persistent high temperature in northern China during this period. In addition, the SSTs in Kuroshio and its extension area (K–KE) in summer 2018 were also the highest since 1961 and the greatest positive SST anomaly in K–KE was favorable for the above normal geopotential height over North China–Northeast China–Japan at 500 hPa, giving rise to the exceptionally high temperature in northern China.
Why Is the East Asian Summer Monsoon Extremely Strong in 2018?    ---Collaborative Effects of SST and Snow Cover Anomalies
Lijuan CHEN, Wei GU, Weijing LI
2019, 33(4): 593-608 [Abstract]( 227 ) HTML PDF (7572 KB)  ( 225 Supplemental Material
Abstract:In 2018, summer precipitation was above normal in North and Northwest China and below normal around the Yangtze River valley, due to an extremely strong East Asian summer monsoon (EASM). The atmospheric circulation anomalies in East Asia and key external forcing factors that influence the EASM in 2018 are explored in this paper. The results show that there existed an anomalous cyclonic circulation near the Philippines, while the western Pacific subtropical high was located more northward than its normal position. In the mid–high latitudes, a negative geopotential height anomaly center was found near the Ural Mountains, suppressing the blocking activity. Under such a circulation pattern, precipitation near the Yangtze River valley decreased because local divergence and subsidence intensified, whereas precipitation in northern China increased due to large amounts of water vapor transport by anomalously strong southerly winds. Further analyses reveal that the strong EASM circulation in 2018 might result from the joint influences of several external forcing factors. The weak La Niña event that started from October 2017, the positive North Atlantic Tripolar mode (NAT) in spring 2018, and the reduced snow cover over the Tibetan Plateau in winter 2017/18 all collaboratively contributed to formation of the cyclonic circulation anomaly near the Philippines, leading to the extremely strong EASM. Especially, the positive NAT and the reduced Tibetan snow cover may have caused the negative geopotential height anomaly near the Ural Mountains, in favor of a strong EASM. The above external factors and their reinforcing impacts on the EASM are further verified by two groups of similar historical cases.
Extremely Active Tropical Cyclone Activities over the Western North Pacific and South China Sea in Summer 2018: Joint Effects of Decaying La Niña and Intraseasonal Oscillation
Lijuan CHEN, Zhensong GONG, Jie WU, Weijing LI
2019, 33(4): 609-626 [Abstract]( 130 ) HTML PDF (4144 KB)  ( 193 Supplemental Material
Abstract:In summer 2018, a total of 18 tropical cyclones (TCs) formed in the western North Pacific (WNP) and South China Sea (SCS), among which 8 TCs landed in China, ranking respectively the second and the first highest since 1951. Most of these TCs travelled northwest to northward, bringing in heavy rainfall and strong winds in eastern China and Japan. The present study investigates the impacts of decaying La Niña and intraseasonal oscillation (ISO) on the extremely active TCs over the WNP and SCS in summer 2018 by use of correlation and composite analyses. It is found that the La Niña episode from October 2017 to March 2018 led to above-normal sea surface temperature (SST) over central-western Pacific, lower sea level pressure and 500-hPa geopotential height over WNP, and abnormally strong convective activities over the western Pacific in summer 2018. These preceding oceanic thermal conditions and their effects on circulation anomalies are favorable to TC genesis in summer. Detailed examination reveals that the monsoon trough was located further north and east, inducing more TCs in northern and eastern WNP; and the more eastward WNP subtropical high as well as the significant wave train with a "− + − +" height anomaly pattern over the midlatitude Eurasia-North Pacific region facilitated the northwest to northward TC tracks. Further analyses reveal that two successively active periods of Madden-Julian Oscillation (MJO) occurred in summer 2018 and the boreal summer intraseasonal oscillation (BSISO) was also active over WNP, propagating northward significantly, corresponding to the more northward TC tracks. The MJO was stagnant over the Maritime Continent to western Pacific, leading to notably enhanced convection in the lower troposphere and divergence in the upper troposphere, conducive to TC occurrences. In a word, the extremely active TC activities over the WNP and SCS in summer 2018 are closely linked with the decaying La Niña, and the MJO and BSISO; their joint effects result in increased TC occurrences and the TC tracks being shifted more northwest to northward than normal.
Representation of the Madden-Julian Oscillation in CAMS-CSM
Pengfei REN, Li GAO, Hong-Li REN, Xinyao RONG, Jian LI
2019, 33(4): 627-650 [Abstract]( 332 ) HTML PDF (8392 KB)  ( 393 Supplemental Material
Abstract:The Madden-Julian Oscillation (MJO) has a significant impact on global weather and climate and can be used as a predictability resource in extended-term forecasting. We evaluate the ability of the Chinese Academy of Meteorological Sciences Climate System Model (CAMS-CSM) to represent the MJO by using the diagnostic method proposed by the US Climate Variability and Predictability Program (CLIVAR) MJO Working Group (MJOWG). In general, the model simulates some major characteristics of MJO well, such as the seasonality characteristics and geographical dependence, the intensity of intraseasonal variability (ISV), dominant periodicity, propagation characteristics, coherence between outgoing longwave radiation (OLR) and wind, and life cycle of MJO signals. However, there are a few biases in the model when compared with observational/reanalyzed data. These include an overestimate of precipitation in the convergence zone of the North and South Pacific, a slightly weaker eastward propagation, and a shift in the dominant periodicity toward lower frequencies with slower speeds of eastward propagation. The model gives a poor simulation of the northward propagation of MJO in summer and shows less coherence between the MJO convection and wind. The role of moistening in the planetary boundary layer (PBL) in the eastward/northward propagation of MJO was also explored. An accurate representation of the vertical titling structure of moisture anomalies in CAMS-CSM leads to moistening of the PBL ahead of convection, which accounts for the eastward/northward propagation of MJO. Poor simulation of the vertical structure of the wind and moisture anomalies in the western Pacific leads to a poor simulation of the northward propagation of MJO in this area. Budget analysis of the PBL integral moisture anomalies shows that the model gives a good simulation of the moisture charging process ahead of MJO convection and that the zonal advection of moisture convergence term has a primary role in the detour of MJO over the Maritime Continent.
Performance of CAMS-CSM in Simulating the Shortwave Cloud Radiative Effect over Global Stratus Cloud Regions: Baseline Evaluation and Sensitivity Test
Yihui ZHOU, Yi ZHANG, Xinyao RONG, Jian LI, Rucong YU
2019, 33(4): 651-665 [Abstract]( 289 ) HTML PDF (2903 KB)  ( 211 Supplemental Material
Abstract:The ability of climate models to correctly reproduce clouds and the radiative effects of clouds is vitally important in climate simulations and projections. In this study, simulations of the shortwave cloud radiative effect (SWCRE) using the Chinese Academy of Meteorological Sciences Climate System Model (CAMS-CSM) are evaluated. The relationships between SWCRE and dynamic-thermodynamic regimes are examined to understand whether the model can simulate realistic processes that are responsible for the generation and maintenance of stratus clouds. Over eastern China, CAMS-CSM well simulates the SWCRE climatological state and stratus cloud distribution. The model captures the strong dependence of SWCRE on the dynamic conditions. Over the marine boundary layer regions, the simulated SWCRE magnitude is weaker than that in the observations due to the lack of low-level stratus clouds in the model. The model fails to simulate the close relationship between SWCRE and local stability over these regions. A sensitivity numerical experiment using a specifically designed parameterization scheme for the stratocumulus cloud cover confirms this assertion. Parameterization schemes that directly depict the relationship between the stratus cloud amount and stability are beneficial for improving the model performance.
Cloud Radiative Feedbacks during the ENSO Cycle Simulated by CAMS-CSM
Lin CHEN, Lijuan HUA, Xinyao RONG, Jian LI, Lu WANG, Guo ZHANG, Ming SUN, Zi'an GE
2019, 33(4): 666-677 [Abstract]( 192 ) HTML PDF (2581 KB)  ( 216 Supplemental Material
Abstract:This study evaluated the simulated cloud radiative feedbacks (CRF) during the El Niño–Southern Oscillation (ENSO) cycle in the latest version of the Chinese Academy of Meteorological Sciences climate system model (CAMS-CSM). We conducted two experimental model simulations:the Atmospheric Model Intercomparison Project (AMIP), forced by the observed sea surface temperature (SST); and the preindustrial control (PIcontrol), a coupled run without flux correction. We found that both the experiments generally reproduced the observed features of the shortwave and longwave cloud radiative forcing (SWCRF and LWCRF) feedbacks. The AMIP run exhibited better simulation performance in the magnitude and spatial distribution than the PIcontrol run. Furthermore, the simulation biases in SWCRF and LWCRF feedbacks were linked to the biases in the representation of the corresponding total cloud cover and precipitation feedbacks. It is interesting to further find that the simulation bias originating in the atmospheric component was amplified in the PIcontrol run, indicating that the coupling aggravated the simulation bias. Since the PIcontrol run exhibited an apparent mean SST cold bias over the cold tongue, the precipitation response to the SST anomaly (SSTA) changes during the ENSO cycle occurred towards the relatively warmer western equatorial Pacific. Thus, the corresponding cloud cover and CRF shifted westward and showed a weaker magnitude in the PIcontrol run versus observational data. In contrast, the AMIP run was forced by the observational SST, hence representing a more realistic CRF. Our results demonstrate the challenges of simulating CRF in coupled models. This study also underscores the necessity of realistically representing the climatological mean state when simulating CRF during the ENSO cycle.
Contrast of Evolution Characteristics of Boreal Summer and Winter Intraseasonal Oscillations over Tropical Indian Ocean
Qingchi ZHANG, Tim LI, Jia LIU
2019, 33(4): 678-694 [Abstract]( 165 ) HTML PDF (11460 KB)  ( 2552 Supplemental Material
Abstract:A most striking summer-winter difference of evolution of the intraseasonal oscillation (ISO) over the equatorial Indian Ocean is a quasi-stationary oscillation in boreal summer but eastward propagation in boreal winter. This feature is consistent with the observational fact that maximum ISO variance appears only in the eastern Indian Ocean in boreal summer while it appears across the entire basin in boreal winter. The cause of the distinctive propagation and initiation characteristics is investigated through the diagnosis of observational and reanalysis data for the period of 1982-2012. It is found that when the ISO convection appears over eastern Indian Ocean, a positive (negative) moisture tendency appears to the east of the convection in boreal winter (summer). It is the moisture tendency difference that is responsible for different propagation behavior in the summer and winter. A further diagnosis of the moisture budget indicates that the major difference lies in anomalous moisture advection by the mean flow. In addition, air-sea interaction also plays a role. While boreal winter ISO starts over western Indian Ocean, boreal summer ISO is initiated over central-eastern equatorial Indian Ocean, due to boundary layer moistening. The moisture increase is caused primarily by the horizontal advection of mean specific humidity by anomalous easterlies induced by preceding suppressed-phase ISO over eastern Indian Ocean. Besides, a delayed SST feedback also plays a role. The overall difference of ISO evolution between the summer and winter is regulated by the seasonal mean state including the mean SST and water vapor content.
Verification of Fengyun-3D MWTS and MWHS Calibration Accuracy Using GPS Radio Occultation Data
Xueyan HOU, Yang HAN, Xiuqing HU, Fuzhong WENG
2019, 33(4): 695-704 [Abstract]( 184 ) HTML PDF (1850 KB)  ( 205 Supplemental Material
Abstract:The newly launched Fengyun-3D (FY-3D) satellite carries microwave temperature sounder (MWTS) and microwave humidity sounder (MWHS), providing the global atmospheric temperature and humidity measurements. It is important to assess the in orbit performance of MWTS and MWHS and understand their calibration accuracy before using them in numerical weather prediction and many other applications such as hurricane monitoring. This study aims at quantifying the biases of MWTS and MWHS observations relative to the simulations from the collocated Global Positioning System (GPS) radio occultation (RO) data. Using the collocated FY-3C Global Navigation Satellite System Occultation Sounder (GNOS) RO data under clear-sky conditions as inputs to Community Radiative Transfer Model (CRTM), brightness temperatures and viewing angles are simulated for the upper level sounding channels of MWTS and MWHS. In order to obtain O-B statistics under clear sky conditions, a cloud detection algorithm is developed by using the two MWTS channels with frequencies at 50.3 and 51.76 GHz and the two MWHS channels with frequencies centered at 89 and 150 GHz. The analysis shows that for the upper air sounding channels, the mean biases of the MWTS observations relative to the GPS RO simulations are negative for channels 5-9, with absolute values < 1 K, and positive for channels 4 and 10, with values < 0.5 K. For the MWHS observations, the mean biases in brightness temperature are negative for channels 2-6, with absolute values < 2.6 K and relatively small standard deviations. The mean biases are also negative for channels 11-13, with absolute values < 1.3 K, but with relatively large standard deviations. The biases of both MWTS and MWHS show scan-angle dependence and are asymmetrical across the scan line. The biases for the upper air MWTS and MWHS sounding channels are larger than those previously derived for the Advanced Technology Microwave Sounder.
Comparisons of AGRI/FY-4A Cloud Fraction and Cloud Top Pressure with MODIS/Terra Measurements over East Asia
Tao WANG, Jiali LUO, Jinglin LIANG, Baojian WANG, Wenshou TIAN, Xiaoyan CHEN
2019, 33(4): 705-719 [Abstract]( 201 ) HTML PDF (7335 KB)  ( 188 Supplemental Material
Abstract:Fengyun-4A (FY-4A), the second generation of China's geostationary meteorological satellite, provides high spatiotemporal resolution cloud products over East Asia. In this study, cloud fraction (CFR) and cloud top pressure (CTP) products in August 2017 derived from the Advanced Geosynchronous Radiation Imager (AGRI) aboard FY-4A (AGRI/FY-4A) are retrospectively compared with those from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Terra (MODIS/Terra) over East Asia. To avoid possible errors in the comparison caused by the lower temporal coverage of MODIS/Terra products compared to that of AGRI/FY-4A over the same region and to account for time lags between observations of the two instruments, we construct datasets of AGRI/FY-4A CFR and CTP to match those of MODIS/Terra in each scan over East Asia in August 2017. Results show that the CFR and CTP datasets of the two instruments generally agree well, with the linear correlation coefficients (R) between CFR (CTP) data of 0.83 (0.80) regardless of time lags. Though longer time lags contribute to the worse consistency between CFR (CTP) data derived from observations of the two instruments in most cases, large CFR/CTP discrepancies do not always match with long time lags. Large CFR discrepancies appear in the vicinity of the Tibetan Plateau (TP; 28°-45°N, 75°-105°E). These differences in the cloud detection by the two instruments largely occur when MODIS/Terra detects clear-sky while AGRI/FY-4A detects higher values of CFR, and this accounts for 61% of the CFR discrepancy greater than 50% near the TP. In the case of CTP, the largest discrepancies appear in the eastern Iranian Plateau (IP; 25°-45°N, 60°-80°E), where there are some samples with long time lags (20-35 min) and fewer daily data samples are available for computing monthly means compared to other regions since there are many clear-sky data samples there during the study period.
Performance of BCC-CSM Models with Different Horizontal Resolutions in Simulating Extreme Climate Events in China
Linxiao WEI, Xiaoge XIN, Chan XIAO, Yonghua LI, Yao WU, Hongyu TANG
2019, 33(4): 720-733 [Abstract]( 158 ) HTML PDF (30432 KB)  ( 192 Supplemental Material
Abstract:In this study, the performance of the Beijing Climate Center (BCC) Climate System Model version 1.1 (BCC-CSM1.1) (280-km resolution) and the BCC-CSM1.1m (110-km resolution) in simulating extreme climate events over China in the last 40 years is compared. Both models capture the main spatial distribution features of heavy precipitation (R95T), the number of consecutive wet days (CWD), the annual count of days with precipitation ≥ 1 mm (R1), the maximum consecutive 5-day precipitation (Rx5), and the numbers of frost days (FD) and summer days (SU). The BCC-CSM1.1m has a better ability to simulate the detailed distribution of extreme climate events than the BCC-CSM1.1, including R95T, CWD, R1, and the simple precipitation intensity index (SDⅡ). However, the BCC-CSM1.1m does not show an improvement in simulating the number of days with extreme precipitation (R90N), the number of consecutive dry days (CDD), the heat wave duration index (HWDI), the warm day frequency (TX90P), and cold night frequency (TN10P). This indicates that the simulation of the R95T, CWD, R1, and SDⅡ climate events is more sensitive to the resolution of the model. The improved BCC-CSM1.1m is used to explore the projection of extreme climate change in China during the 21st century under the RCP4.5 (Representative Concentration Pathways) and RCP8.5 scenarios. The results show that extreme precipitation will increase dramatically over North and Southwest China in the late 21st century. The CWD index will decrease on the Tibetan Plateau and in northeastern and central China and will increase in other parts of China; R1 will increase in northern China and decrease in southern China; Rx5 will increase dramatically in southern China; FD will decrease and SU will increase over China in the late 21st century under both emission scenarios, with larger amplitudes in RCP8.5.
Simulation Study of Cloud Properties Affected by Heterogeneous Nucleation Using the GRAPES_SCM during the TWP-ICE Campaign
Zhe LI, Qijun LIU, Zhanshan MA, Jiong CHEN, Qingu JIANG
2019, 33(4): 734-746 [Abstract]( 137 ) HTML PDF (3017 KB)  ( 154 Supplemental Material
Abstract:This study used the Global/Regional Assimilation and PrEdiction System Single-Column Model (GRAPES_SCM) to simulate monsoon precipitation with deep convective cloud and associated cirrus during the Tropical Warm Pool International Cloud Experiment (TWP-ICE), especially during the active and suppressed monsoon periods. Four cases with different heterogeneous nucleation parameterizations were simulated by using the ensemble method. All simulations clearly separated the active and suppressed monsoon periods, and they reproduced the major characteristics of monsoonal cloud such as the total cloud hydrometeor mixing ratio distribution,and precipitation and radiation properties. The results showed that the number concentration production rate of different heterogeneous nucleation parameterizations varied substantially under the given temperature and water vapor mixing ratio. However, ice formation and precipitation during the monsoon period were affected only slightly by the different heterogeneous nucleation parameterizations. This study also captured clear competition between different ice formation processes.
Evaluation of TIGGE Daily Accumulated Precipitation Forecasts over the Qu River Basin, China
Li LIU, Chao GAO, Qian ZHU, Yue-Ping XU
2019, 33(4): 747-764 [Abstract]( 144 ) HTML PDF (1581 KB)  ( 201 Supplemental Material
Abstract:Quantitative precipitation forecasts (QPFs) provided by three operational global ensemble prediction systems (EPSs) from the THORPEX (The Observing System Research and Predictability Experiment) Interactive Grand Global Ensemble (TIGGE) archive were evaluated over the Qu River basin, China during the plum rain and typhoon seasons of 2009-13. Two post-processing methods, the ensemble model output statistics based on censored shifted gamma distribution (CSGD-EMOS) and quantile mapping (QM), were used to reduce bias and to improve the QPFs. The results were evaluated by using three incremental precipitation thresholds and multiple verification metrics. It is demonstrated that QPFs from NCEP and ECMWF presented similarly skillful forecasts, although the ECMWF QPFs performed more satisfactorily in the typhoon season and the NCEP QPFs were better in the plum rain season. Most of the verification metrics showed evident seasonal discriminations, with more satisfactory behavior in the plum rain season. Lighter precipitation tended to be overestimated, but heavier precipitation was always underestimated. The post-processed QPFs showed a significant improvement from the raw forecasts and the effects of post-processing varied with the lead time, precipitation threshold, and EPS. Precipitation was better corrected at longer lead times and higher thresholds. CSGD-EMOS was more effective for probabilistic metrics and the root-mean-square error. QM had a greater effect on removing bias according to bias and categorical metrics, but was unable to warrant reliabilities. In general, raw forecasts can provide acceptable QPFs eight days in advance. After post-processing, the useful forecasts can be significantly extended beyond 10 days, showing promising prospects for flood forecasting.
Dominant Synoptic Patterns and Their Relationships with PM2.5 Pollution in Winter over the Beijing-Tianjin-Hebei and Yangtze River Delta Regions in China
Yuzhi LIU, Bing WANG, Qingzhe ZHU, Run LUO, Chuqiao WU, Rui JIA
2019, 33(4): 765-776 [Abstract]( 155 ) HTML PDF (4701 KB)  ( 731 Supplemental Material
Abstract:This paper concerns about the episodes of PM2.5 pollution that frequently occur in China in winter months. The severity of PM2.5 pollution is strongly dependent on the synoptic-scale atmospheric conditions. We combined PM2.5 concentration data and meteorological data with the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT4) to investigate the dominant synoptic patterns and their relationships with PM2.5 pollution over the Beijing-Tianjin-Hebei (BTH) and Yangtze River Delta (YRD) regions in the winters of 2014-17. The transport of PM2.5 from the BTH to YRD regions was examined by using cluster analysis and HYSPLIT4. It is found that the level of PM2.5 pollution over the BTH region was higher than that over the YRD region. The concentration of PM2.5 in the atmosphere was more closely related to meteorological factors over the BTH region. The episodes of PM2.5 pollution over the BTH region in winter were related to weather patterns such as the rear of a high-pressure system approaching the sea, a high-pressure field, a saddle pressure field, and the leading edge of a cold front. By contrast, PM2.5 pollution episodes in the YRD region in winter were mainly associated with the external transport of cold air, a high-pressure field, and a uniform pressure field. Cluster analysis shows that the trajectories of PM2.5 were significantly different under different weather patterns. PM2.5 would be transported from the BTH to the YRD within 48 h when the PM2.5 pollution episodes were associated with three different kinds of weather patterns:the rear of a high-pressure system approaching the sea, the high-pressure field, and the leading edge of a cold front over the BTH region. This suggests a possible method to predict PM2.5 pollution episodes based on synoptic-scale patterns.
Uncertainties in the Effects of Climate Change on Maize Yield Simulation in Jilin Province: A Case Study
Yanxia ZHAO, Chunyi WANG, Yi ZHANG
2019, 33(4): 777-783 [Abstract]( 154 ) HTML PDF (670 KB)  ( 186 Supplemental Material
Abstract:Measuring the impacts of uncertainties identified from different global climate models (GCMs), representative concentration pathways (RCPs), and parameters of statistical crop models on the projected effects of climate change on crop yields can help to improve the availability of simulation results. The quantification and separation of different sources of uncertainty also help to improve understanding of impacts of uncertainties and provide a theoretical basis for their reduction. In this study, uncertainties of maize yield predictions are evaluated by using 30 sets of parameters from statistical crop models together with eight GCMs with reference to three emission scenarios for Jilin Province of northeastern China. Regression models using replicates based on bootstrap resampling reveal that yields are maximized when the optimum average growing season temperature is 20.1℃ for 1990-2009. The results of multi-model ensemble simulations show a maize yield reduction of 11%, with 75% probability for 2040-69 relative to the baseline period of 1976-2005. We decompose the variance so as to understand the relative importance of different sources of uncertainty, such as GCMs, RCPs, and statistical model parameters. The greatest proportion of uncertainty (> 50%) is derived from GCMs, followed by RCPs with a proportion of 28% and statistical crop model parameters with a proportion of 20% of total ensemble uncertainty.
Perturbations in Earth's Atmosphere over An Indian Region during the Total Solar Eclipse on 22 July 2009
S. B. Surendra PRASAD, Vinay KUMAR, K. Krishna REDDY, S. K. DHAKA, Shristy MALIK, M. Venkatarami REDDY, U. Murali KRISHNA
2019, 33(4): 784-796 [Abstract]( 225 ) HTML PDF (887 KB)  ( 609 Supplemental Material
Abstract:During a total solar eclipse (TSE) on 22 July 2009, atmospheric perturbations were monitored from the surface to thermosphere to understand TSE's impact on the meteorological (temperature, relative humidity, wind speed, and wind direction) and chemical (O3 and NOx) parameters around Kadapa (14.28°N, 78.42°E), a tropical semi-arid region of India. For this purpose, an experiment was conducted at Yogi Vemana University Campus, Kadapa, India, to measure the temperature, wind speed, wind direction, and concentrations of ozone (O3), NO, NO2, and NOx by using the automatic weather station (AWS) and O3 analyzer. On the eclipse day (22 July 2009), the surface observations at Kadapa showed a reduction in temperature (about 1.1℃) because of the solar insulation. Comparison of the thermal, dynamical (wind), and chemical parameters on the TSE day with control days[preceding (21 July 2009) and succeeding (23 July 2009) the TSE] illustrated the influence of solar eclipse. During the eclipse period, the O3 mixing ratio decreased, while NO2 and NOx increased; however, NO remained unchanged. In addition, radio occultation (RO) temperature profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)/Formosat Satellite Mission (FORMOSAT-3) and Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) satellites were utilized to understand the impact of TSE on dynamics of the middle and upper atmosphere from tropopause to the thermosphere. High vertical resolution COSMIC observations revealed that during the solar eclipse, tropopause was cooler with twin peaks (double tropopause). The lower thermosphere between 110 and 130 km became warmer during the TSE, which might be caused by the dynamical response of the atmosphere in this region to the solar eclipse. The experimental data have provided very fine-scale variations of the atmospheric parameters both in time and height and also constituted a new set of results on TSE for further research.
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